Stellites are a class of alloys used as hard facing materials and tools. They can contain up to about 65% by weight of cobalt with varying amounts of chromium, tungsten, and nickel with lesser amounts of iron, carbon, and silicon. In the fabrication of these tools or facing materials a large amount of material has to be removed by grinding or machining. The cobalt in this removed scrap material can be lost if it is not recovered from the material.
To recover cobalt from this type of material, the material, is dissolved in acids or oxidized with heat. However, because stellites are alloys of chromium, they are oxidation resistant and do not lend themselves to any simple recovery process.
Dissolution in acids as hydrochloric acid and sulfuric acid produces excessive amounts of hydrogen which is dangerous because of its explosive nature. Also, acid dissolution dissolves all the elements making a further separation necessary. It is possible to eliminate the evolution of hydrogen by first converting the stellites to oxides. However, again they are not easy to oxidize being oxidation resistant. Also, during any oxidation, the cobalt unites with the chromium producing cobalt chromite which is analogous to iron chromate, the natural ore of chromium. Cobalt chromite is acid insoluble making the recovery of cobalt with acid nearly impossible.
Reaction of stellites with sodium carbonate is hard to control and usually does not give a complete reaction with the chromium.